July 10, 2014

Alaska’s Denali National Park Holds 70M-Year-Old Dinosaur Footprints

Denali National Park covers over six million acres of land in the center of Alaska. One road bisects the park, leading from taiga forests to the highest mountain in North America, Mount McKinley. Today, many species of wildlife roam freely through the park.

According to a new study led by the Perot Museum of Nature and Science, Denali was once home to large herds of duck-billed dinosaurs called hadrosaurs, as well.

A remarkable tracksite, discovered originally in 2007 on the last day of a US National Park Service survey, demonstrates that hadrosaurs not only lived in multi-generational herds, but lived year round in the ancient high-latitude polar ecosystem.

During the original survey to the as-yet unexplored Cretaceous Cantwell Formation in Denali NP, the trio came upon a wealth of tracks on the steep side of a mountain near Cabin Peak, on the northeast side of the park.

“Without question, Denali is one of the best dinosaur footprint localities in the world, but what we found that last day was incredible – so many tracks, so big, and so well preserved,” said Fiorillo. “Many had skin impressions so we could even see what the bottom of their feet looked like. And there were lots of invertebrate traces – the tracks of bugs, worms, larvae and more – which were important to us because they showed an ecosystem existed during the warm parts of the years.”

Fiorillo is convinced that dinosaurs lived at polar latitudes year-round during the Late Cretaceous Period (approximately 70 million years ago), and the tracksite adds to the growing evidence he has collected to support this conviction.

"Even back then the high latitudes were biologically productive and could support big herds of pretty big animals," said Fiorillo.

“The Denali tracksite is extremely significant to the reconstruction of this Cretaceous high latitude polar ecosystem as it demonstrates higher annual temperatures compared to the present-day climate. The hadrosaur tracks show specifically where they lived and how they acted as an extended family. The burrows and trails of mud-loving beetles, mole crickets, midge fly larvae, and other sediment-dwelling beasties demonstrate that the whole cast of characters left their traces of life in the river bank sediments during the warm summer months—frozen in time, waiting to be discovered!" said Hasiotis

The site contained thousands of tracks from four different sizes of hadrosaurs—baby, juevenile, sub-adult and adult. These ranged in size from five to 24 inches. So many hadrosaurs walked this area that the researchers were unable to pull tracks from a single individual, rather they had to count the tracks and group them by size. Eighty percent of the tracks were in the adult range, while another 13 percent were from babies less than a year old. Juveniles comprised only three percent of the tracks, leading the researchers to suggest that the young underwent a rapid growth spurt, spending only a short amount of time as babies. Prior research with hadrosaur bone fossils also bear out this theory.

“This is one of the greatest dinosaur tracksites in the world in terms of size, number, and quality. We could see how hadrosaurs walked, ran, or slipped on muddy surface. Footprints were so vivid that we almost could see and smell them,” said Kobayashi. “We were so excited when we found tiny, baby footprints, because we instantly knew this was the evidence to support the polar hadrosaurs survived through winters and lived as a herd to protect each other like other mammals do.”

The site was in danger of destruction from earthquake damage. If such a quake occurred, the single bedding plane of tracks would crumble and slide down the mountain into the nearby river. Denali NP officials helped the paleontologists to remove and preserve the specimens before such a catastrophic loss could happen.

Molds of the tracks were transported to the Perot Museum where Ronald S. Tykoski, PhD, a fossil preparator, began to meticulously craft casts of the tracks.

Considered to be the "cow" or "buffalo" of the Cretaceous Period, duck-billed dinosaurs represent the most common fossils recovered from this time period. A wide range of species can be found on several continents.